Sorry I can't post a pic, but the old fashioned adjustable wrenches with the jaws at right angles to the handle are good for making these from, and of course they are adjustable for different sized retainers. The larger the wrench the better, 12 to 15 inches would be about right and you can always slip a bit of pipe over the handle for a bit of extra leverage.
Drill a hole into the end of each jaw about an inch deep to take an approriate sized shank from a high tensile bolt, thread the hole to suit the bolt, screw in tight and cut off with about 5mm of bolt shank exposed.
Get a bolt that is only threaded for the first inch so the shank that ends up exposed is free of thread, or shorten the threaded section before installation.
And the wrench can even still be used for it's original purpose.
I hope I have managed to make myself clear, as they say, a picture is worth a thousand poorly chosen words.